Where the numbers come from

The Confidence meter

Each plant’s page carries a meter of one to three bars, for how sure we are of its figures. It rests mostly on how many kinds of caterpillar the plant feeds, because that number drives the wildlife ranking:

• High: counted from a dataset for its region, with a cited source for where it grows wild.
• Medium: a published figure for its genus (its closest group of related plants), or our estimate from a relative.
• Low: rough, or with nothing cited for where it grows wild.

It rates our figures, not the plant. A plant rated low can be just as good a choice.

Checked against Kew

Kew’s World Checklist, kept by the Royal Botanic Gardens in London, records where every plant grows wild. Each plant’s page says whether it agrees the plant is native where you are, and when we checked: a green check when it agrees, a caution mark when it doesn’t. Disagreement isn’t a mistake on its own: Kew records whole states and provinces, and a regional flora can know better. What “native” means here.

Checked against regional floras

In the Pacific Northwest, each plant is also checked against two checklists written by the region’s own botanists: the Burke Museum’s, at the University of Washington, and OregonFlora’s, at Oregon State. They know the region better than Kew does, and they don’t always agree with each other. Where they don’t, the page says who said what.